The most common type of inject printer uses thermal drop-on-demand technology, first discovered in 1977 by a Canon engineer. During the same period, an HP engineer started developing the same technology borrowing on the mechanism of a coffee percolator. The basic idea is that a number of chambers each containing a heating element, heat ink causing it to vaporize and form a bubble. This bubble is then propelled onto paper due to the pressure that develops in the chamber marking one of the dots that compose the bigger picture.